The overall objective of this project is the elucidation of the nature and role of iron-sulfur in membrane-bound energy-transducing systems, with emphasis on their involvement in photosynthetic systems. Iron-sulfur proteins have recently been found in membrane-bound form in both the mitochondrion and the chloroplast. There are several different iron-sulfur centers in chloroplasts but their precise site(s) of function is not yet known. One goal for the current project is to determine the involvement of these iron-sulfur centers in the various photosynthetic electron-transfer reactions. Particular emphasis will be placed on the possible involvement of these centers in ATP-generating reactions. A second goal of this project is the characterization of the bound chloroplast iron-sulfur proteins in the isolated state. One protein has been obtained in pure form and preliminary characterization of a second high-potential iron-sulfur protein is being undertaken. It is anticipated that these structural studies will yield significant information on the chemical nature of this class of bound iron-sulfur proteins. BIBLIOGRAPHIC REFERENCES: Malkin, R. (1975) Photochemical properties of a Photosystem I subchloroplast fragment. Arch. Biochem. Biophys. 169, 77-83. Knaff, D.B., and Malkin, R. (1976) Iron-sulfur proteins in the green photosynthetic bacterium Chlorobium. Biochim. Biophys. Acta, in press 1976.